Members of the prosecution team from the Arapahoe County District Attorney's Office leave the Century 16 theater after spending more than an hour there in Aurora, Colo., July 24, 2012. Jury selection begins Tuesday in the trial of accused gunman James Holmes in the shooting at the Denver-area movie theater showing 'The Dark Knight Rises' that left 12 dead and 70 wounded. Prosecutors are seeking the death penalty.

Ed Andrieski/AP/File

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Just weeks after the start of the Boston Marathon bombing trial, another high-profile trial is set to begin Tuesday, as jury selection begins in Denver for the Aurora, Colo., massacre.

James Holmes has pleaded not guilty by reason of insanity to multiple counts of murder and attempted murder. Mr. Holmes’s family and defense team maintain that he was experiencing a psychotic episode and was unable to tell right from wrong when he opened fire at a midnight showing of the new "Batman" movie in Aurora on July 20, 2012. Twelve people died in the attack and another 70 were injured.

Judge Carlos Samour Jr. has called 9,000 Arapahoe County, Colo., residents to potentially serve as jurors. The process of whittling that unprecedented jury pool down to 12 jurors and 12 alternates could take as long as six months.

There are several similarities in the cases unfolding in Boston and Denver. Both attacks involved the indiscriminate killing of multiple people in a very public setting. Both have been widely publicized in the local and national media. And both defendants could face the death penalty if found guilty.

The initial days of juror selection in the trial of accused Boston bomber Dzhokhar Tsarnaev have provided a glimpse of just how difficult impaneling an impartial jury for such heinous and high-profile crimes can be. The defense has raised concerns that potential jurors will have already convicted Mr. Tsarnaev in their minds, while some jurors have maintained that their personal convictions would prohibit them from imposing the death penalty.

Holmes’s case is slightly different from Tsarnaev’s because of the plea of insanity. Holmes's defense team is not expected to dispute the fact that he killed 12 people. They are instead arguing that he should be placed in a state psychiatric facility, rather than go to jail or be put to death.

An insanity plea in itself is rather controversial. Because the plea is rare and defined differently from state to state, it is not well understood by the public, according to an analysis of the plea in this case published in the Journal of Law and Social Deviance.

Several states have declared the plea to be unconstitutional and bar it altogether. Some states place the burden of proof of insanity on the defense. In Colorado, however, it is the prosecution's responsibility to prove that the defendant is sane enough to be held fully responsible.

“Many people believe that the insanity defense is a loophole that allows guilty defendants to ‘go free,’ " write legal experts Kathleen Bantley and Susan Koski in the analysis. “In one survey, sixty-six percent of respondents believed that the insanity defense should not be available.”

Some legal analysts argue that this defense is protected by the 14th Amendment’s due process clause or the Eighth Amendment’s ban on cruel and unusual punishment. The US Supreme Court was asked – and declined – to weigh in on the issue in 2012.

If Holmes is found guilty, the jury will then have to decide if he should be put to death. Coloradans aren’t as opposed to the death penalty as many Massachusetts residents are: A poll conducted by The Denver Post found that 68 percent of Coloradans favor the death penalty. However, since the death penalty was reinstated in Colorado in 1975, only one person has actually been put to death.

Holmes's defense team has reportedly hired a victim-outreach specialist to solicit victims and victims’ family members to testify against the death penalty. A minister in Boston who has worked closely with victims of the Boston Marathon bombings told the Monitor in December that the same specialist had been reaching out to victims involved in that attack as well.